Topic 8: neuron

Nervous system consists of

Peripheral NS and Central Nervous System

Peripheral NS consists of

Sensory Division and Efferent Division

Sensory Division

Sends information to the CNS through afferent neurons

Efferent Division

Takes info from CNS to target cells via efferent neurons

Neurons carry

Electrical signals

Dendrites:

receive incoming signals

Cell body of neuron is the

Control center

Axons =

carry outgoing signals

Label

Neuron function cells:

Afferent, Efferent, and interneurons

Axonal transport: Anterograde transport

Moves vesicles and mito from cell body to axon terminal

Retrograde transport

Returns old cellular components from the axon terminal to the cell body for recycling

Synapse location is

region where an axonal terminal meets target cell

Synaptic cleft:

Connects presynaptic cell and postsynaptic cell

Schwann cells (PNS) and oligodendrocytes (CNS

Wrap around axon and form insulating myelin sheaths

Myelination is the

Process of wrapping an axon with

myelin

Myelin is several

layers of membrane of glial cells

Myelin: lipid content/appearance

High lipid content = glossy-white appearance insulates axon

Node of ranvier

Gaps in insulation

Satellite cells (PNS) =

nonmyelinating Schwann cell

Satellite cells components and their location

Ganglion (outside of CNS) and Nucleus (inside CNS)

Microglia (CNS) =

specialized immune cells

Astrocytes (CNS) =

several subtypes, multiple roles

Ependymal cells =

one source of neural stem cells

Ion movement creates

Electrical signals

Resting membrane potential determined primarily by

K+ concentration gradient

Cell’s resting permeability to:

▪ K+

▪ Na+

▪ Cl-

Memorize

Changes in membrane’s permeability result in

ion movement

ion movement causes

Movement creates an electrical signal

Ions channel named because

Primarily ions pass through

Gated channels ion permeability can be

mechanically, chemically, or voltage-gated

Voltage channels differ from leak channels as

Remain open in the voltage range

Two types of electrical signals:

Graded potentials and action potential

Graded potentials

Varied strength and Used for short distance communication

Action potentials

Very brief, large depolarizations

– Rapid signaling over long distances

Graded Potentials Reflect

Stimulus Strength

Local current flow =

wave of depolarization through cell

Graded potentials lose strength as they move through the cell due to;

Ions may cross membrane (leak) or electrical flow may be impeded (cytoplasmic resistance)

If strong enough, graded potentials reach

reach trigger zone in axon hillock and initial segment

Cell’s excitability =

ability to fire an action potential

Action potentials are

All or nothing

Conduction of action potentials =

high-speed movement of AP along axon

Action Potentials signals are

Wave of electrical signal at constant amplitude

Depolarization

Positive charge spreads along adjacent sections of axon by local current flow

Depolarization dependent

On voltage-gated Na+ channels

The local current flow causes

new section of membrane to depolarize

Backward flow cannot occur because

Because Na+ channels inactivated

Absolute refractory period

Membrane cannot produce another AP Because Na+ channels are inactivated

Relative refractory period

– When VG K+ channels are open, More difficult to depolarize to threshold

Without a myelin sheath: After axon hillock:

Conduction reaches threshold and fire ap

Conduction in an unmyelinated axon NA+ influx

Na+ influx depolarizes adjacent regions to

threshold

NA+ influx in myelinated sheath:

Generates new AP and has slow conduction

Conduction is slower or faster in myelinated neurons?

Faster

Saltatory conduction

Resistance of axon membrane to ion leakage out of the cell

The synapse is the

Cell to cell communication in the nervous system

Synapse connects

Neuron (presynaptic) to another cell (postsynaptic)

Synapse can be

Chemical or electrical

Synaptic transmission in chemicals via

neurotransmitters (NT)

– Electricals rare in PNS

Neurotransmitters are in

Synaptic vesicles inside axon hillock

When action potentials travel down axon to depolarize bouton:

(1) Open VG Ca2+

channels in bouton

(2)Ca2+ driven

in by electro-

chemical

gradient

After release of CA2+ (3)

Vesicles fuse with bouton membrane, Release NT by exocytosis

• Amount of NT released =

frequency of APs

Stringer will release

More neurotransmitters

Action potentials code

duration and magnitude in frequency of action potentials produced

Neurotransmitter Release

Is rapid because vesicles docked at release sites on

bouton before APs arrive

–Docked vesicles inside nt release are part

of fusion complex

Fill in the blank.

Chemically-regulated ion channels open

depolarizing channels and hyperpolarizing channels

Depolarizing channels cause __ and are stimulated by

EPSP

Opening Na+ and Ca2+ channels

Hyperpolarizing channels cause ___

and are stimulated by

IPSP

Opening K+ or Cl- channels

EPSPs and IPSPs summate and

and are graded in magnitude

If postsynaptic Membrane Potential reaches

threshold, new AP generated

Cable properties of neurons cause

Cause EPSPs to fade quickly

Because of cable neurons experience:

–Attenuation, Conduction Delay, Summation

Attenuation:

As signal moves, it gradually weakens

–Conduction Delay:

Signal takes time to reach destination

Summation:

Neurons add up signals

Spatial summation takes place when:

EPSPs from different synapses occur on postsynaptic cellat the same time

Temporal summation takes place when

–EPSPs occur close in time

–EPSPs sum before fading

Synaptic inhibition: Ipsp/ hyperpolarization causes

It to be more difficult to reach threshold

Long term potentiation alters

Synapses

Activity at a synapse induces

sustained changes in quality or quantity of connections

Facilitation

Increase in ease of transmission

Depression

Decrease in ease of transmission